Field of the Invention
The present invention relates to a shift-drum speed change mechanism.
Related Art
Shift-drum speed change mechanisms have been proposed and used as speed change mechanisms that are disposed in the driveline of utility vehicles, all-train vehicles, off-road vehicles, etc.
For example, JP2014-070650A (hereinafter referred to as Patent Document 1, which has a corresponding U.S. application publication No. US 2014/0083228A1) discloses a shift-drum speed change mechanism comprising an operation shaft rotated around the axis; a drum supported by the operation shaft so as to be incapable of relative rotation and provided with, on the outer circumferential surface, a first guide groove for switching between high and low speeds and a second guide groove for switching between forward and reverse; a first shift fork having a first engagement pin inserted into the first guide groove; a second shift fork having a second engagement pin inserted into the second guide groove; a fork shaft supporting the first and second shift forks so as to be movable in the axial direction; a high gear, a low gear, and a reverse/parking gear supported by a power transmission rotating shaft; a first slider that is supported by the power transmission rotating shaft so as to be incapable of relative rotation around the axis and movable in the axial direction between the high gear and the low gear, and is moved in the axial direction by the first shift fork so as to be capable of taking a high-speed position where the first slider is engaged with the high gear, a neutral position where the first slider is not engaged with any of the high and low gears, and a low-speed position where the first slider is engaged with the low gear; and a second slider that is supported by the power transmission rotating shaft so as to be incapable of relative rotation around the axis and movable in the axial direction while facing the reverse/parking gear, and is moved in the axial direction by the second shift fork so as to be capable of taking a reverse/parking position where the second slider is engaged with the reverse/parking gear and a neutral position where the second slider is not engaged with the reverse-parking gear.
The conventional shift-drum speed change mechanism described in Patent Document 1 further has a shift spindle that is rotated around the axis in accordance with manual operation and is operatively connected to the operation shaft, and a parking mechanism operatively connected to the shift spindle.
The shift spindle takes a high-speed position, a low-speed position, a reverse position, and a parking position around the axis, and the parking mechanism brings the reverse/parking gear into a rotation suspended state only when the shift spindle is operated to the parking position.
The first and second guide grooves are configured to provide a high-speed state where the second slider is placed at the neutral position and the first slider is placed at the high-speed position to be engaged with the high gear when the operation shaft is placed at the high-speed position around the axis in accordance with the operation of the shift spindle to the high-speed position; a low-speed state where the second slider is placed at the neutral position and the first slider is placed at the low-speed position to be engaged with the low gear when the operation shaft is placed at the low-speed position around the axis in accordance with the operation of the shift spindle to the low-speed position; a reverse state where the first slider is placed at the neutral position and the second slider is placed at the reverse/parking position to be engaged with the reverse/parking gear when the operation shaft is placed at the reverse position around the axis in accordance with the operation of the shift spindle to the reverse position; and a parking state where the first slider is placed at the neutral position and the second slider is placed at the reverse/parking position to be engaged with the reverse/parking gear that is in a state where the rotation is forcibly suspended by the parking mechanism, when the operation shaft is placed at the parking position around the axis in accordance with the operation of the shift spindle to the parking position.
Meanwhile, when connecting the first or second slider to the corresponding speed change gear, if the circumferential positions of engagement part provided on the slider and engagement part provided on the corresponding speed change gear match, (i.e., if projections or depressions of the engagement part of the slider face depressions or projections of the projection/depression engagement part of the speed change gear), the slider can be immediately connected to the corresponding speed change gear.
Accordingly, an operator can immediately complete the manual operation for placing the operation shaft at the desired speed change position in this case.
However, if the circumferential positions of the engagement part of the slider and the engagement part of the corresponding speed change gear do not match (i.e., if the projections, or the depressions, of the engagement parts of the slider and the speed change member face each other), the slider cannot be pushed to the position where the slider is connected to the corresponding speed change gear.
In such a case, the operator has to continue operating the operation shaft around the axis toward the desired speed change position until the circumferential positions of the engagement parts of the slider and the speed change gear match so that the slider is actually connected to the speed change gear.
Moreover, the conventional shift-drum speed change mechanism disclosed in Patent Document 1 also has room for improvement on the following point.
That is, with the conventional shift-drum speed change mechanism, the operation shaft is retained at the parking/reverse position when the shift spindle is operated from the parking position to the reverse position, and the parking mechanism provides a parking state where the rotation of the reverse/parking gear is forcibly suspended when the shift spindle is placed at the parking position, and provides a reverse state by cancelling the forced suspension of the rotation of the reverse/parking gear when the shift spindle is operated from the parking position to the reverse position.
In this way, the conventional shift-drum speed change mechanism can selectively provide four speed change states of a forward high-speed state, a forward low-speed state, a parking state, and a reverse state by operating the shift spindle around the axis, but is problematic in that the order of the four speed change states are fixed.
More specifically, with the conventional shift-drum speed change mechanism above, for example, the shift spindle is operated from the parking position to the forward high-speed position through the forward low-speed position when the speed change state is changed from the parking state to the forward high-speed state. During the course of this speed change, the forward low-speed state is always reached.
That is, when the shift spindle is operated from the parking position to the forward high-speed position, the forward low-speed position is passed through during the course of this operation. At this time, the first slider is always placed at the forward low-speed position and engaged with the forward low-speed gear so that the shift-drum speed change mechanism arrives at the forward low-speed state.
Thereafter, when the shift spindle passes through the forward low-speed position and then reaches the forward high-speed position, the first slider is moved from the forward low-speed position to the forward high-speed position through the neutral position and is engaged with the forward high-speed gear so that the shift-drum speed change mechanism arrives at the forward high-speed state.
The same applies to the case where the speed change state is changed from the forward high-speed state to the parking state, and in the case where a speed change operation is performed between the forward low-speed state and the reverse state as well, the parking state is always reached during the course of the operation.